China Earthquake a Dam-Induced Disaster?

Wed, 02/04/2009 - 5:56pm

By:

Peter Bosshard

Sichuan earthquake of May 2008

mike at bloggin-ads.com

The devastating earthquake in Sichuan, which took at least 69,000 lives in May 2008, may have been unleashed by the huge Zipingpu Dam. New scientific evidence suggests that the filling of the Zipingpu reservoir may have activated a dormant fault line near the dam site. This is all the more worrisome because the Chinese government plans to shift the center of its dam-building efforts into seismically active regions.

It is well established that large dams can trigger earthquakes through what is called reservoir-induced seismicity. Scientists have produced evidence linking tremors to the raising and lowering of reservoirs for more than 70 dams around the world. Reservoirs can increase the frequency of earthquakes in areas of high seismic activity, and can cause earthquakes to happen in areas that were thought to be seismically inactive.

Zipingpu is a 156-meter-high dam on the Min River, a tributary of the Yangtze. The project, which displaced 33,000 people, was completed with Japanese funding in 2006. Fan Xiao, a chief engineer with the Sichuan Geology and Mineral Bureau, warned about Zipingpu's seismic risks even before the dam was completed. After the disaster, he explained that “Zipingpu has all conditions that provoke reservoir-induced earthquakes,” and said that “we cannot rule out the possibility that building the Zipingpu Dam induced the earthquake because the epicenter is so close to the dam.” (Fan’s interview with the South Urban Daily, like other useful documents on the topic, has been translated by Three Gorges Probe.)

Zipingpu Dam

AP Photo/GeoEye Satellite Image

Christian Klose, a geophysical hazards researcher at Columbia University’s Lamont-Doherty Earth Observatory, found that the fault line that triggered the Sichuan quake had not been active for millions of years. Klose presented his research at a meeting of the American Geophysical Union in San Francisco in December 2008. According to Klose, “the ensemble of geophysical observations suggests that the root cause of triggering the M7.9 Wenchuan earthquake may have stemmed from local and rapid mass changes on the surface.”

In January 2009, a news article on Klose's findings in the journal Science elaborated, “the added weight [of the Zipingpu reservoir] both eased the squeeze on the fault, weakening it, and increased the stress tending to rupture the fault. The effect was 25 times that of a year’s worth of natural stress loading from tectonic motions. (…) When the fault did finally rupture, it moved just the way the reservoir loading had encouraged it to.”

In a separate paper in the Chinese journal Geology and Seismology, Lei Xinglin, a geophysicist at the China Earthquake Administration in Beijing, and four colleagues produced further evidence for the seismic impacts of the Zipingpu Dam. According to the paper, “some clear correlations were verified between the local seismicity and stress change, thus we concluded that the impoundment of Zipingpu clearly affected the local seismicity and it is worthwhile to further study if the effect played a role in triggering the Wenchuan earthquake.” [In November 2009, after this blog was first published, a group of Chinese-American scientists provided further evidence on the link between the Zipingpu Dam and the Sichuan earthquake.]

More research into the cause of the Wenchuan earthquake is needed. What is clear is that the tremor almost broke Zipingpu and other dams. During the quake, the fault line slipped up to seven meters upward. In a story in New Scientist, Fred Pearce describes that “as the tight valley sides juddered, the [Zipingpu Dam] structure was squeezed and ended up to 18 centimeters downstream, and 70 cm lower. The concrete was ripped apart but the core of the dam survived.” According to China’s Ministry of Water Resources, 69 dams were in danger of collapse after the earthquake in Sichuan Province alone, 310 were at “high risk,” and 1,424 posed a “moderate risk.”

At the time of the earthquake, the Zipingpu reservoir was half-empty. Pearce suspects that if the tremor had happened two months later during the monsoon season, “Zipingpu and the other dams would probably have failed,” inundating Dujiangyan, a city of 600,000, and other downstream areas. The reservoir is now empty, awaiting repair of the dam.

The mountains of Southwest China mark the collision of the Indian and Eurasian plates, and are geologically unstable. Yet they are also at the center of current Chinese dam building. The same is true for other hotspots of global dam building in the Himalayas, in Turkey and Iran. After the Sichuan quake, 62 Chinese experts in geology, water management and environmental protection appealed to the authorities in Beijing to “temporarily suspend the approval of big hydro dams in geologically unstable areas in southwest China.” They asked the government to take five measures, including studies on the risks of reservoir–induced seismicity in geologically unstable regions, and on the safety risks posed by cascades of dams to the downstream areas in earthquake-prone regions.

So far, the Chinese authorities have dismissed evidence linking the Zipingpu Dam to the Sichuan quake. Yet the concept of scientific development is a guiding principle of the current government in Beijing. Free scientific research and debate is needed to assess the seismic risks of the massive dam-building program in China and other earthquake-prone countries.